The present invention relates to the manufacture of a strip made of an Fexe2x80x94Ni alloy of the xe2x80x9cxcex3xe2x80x2 and/or xcex3xe2x80x3 structural hardeningxe2x80x9d type and to the strip obtained.
To manufacture articles such as tensioned shadow mask support frames for colour television tubes, strips made of an Fexe2x80x94Ni alloy of the xe2x80x9cxcex3xe2x80x2 and/or xcex3xe2x80x3 structural hardeningxe2x80x9d type, having a low expansion coefficient and a high yield strength after hardening, are used.
The process for manufacturing these frames comprises many operations. First of all, parts are cut from a softened strip, which parts are bent and then assembled by welding so as to obtain a frame. A series of operations are carried out on this frame, intended to blacken it, by forming a layer of oxides, and to harden it and to fasten the shadow mask. During these operations, the frame is subjected to forces at high temperature which may cause creep, possibly resulting in unacceptable deformation or even fracture.
It is the object of the present invention to provide a process which makes it possible to obtain a strip made of an Fexe2x80x94Ni alloy of the xe2x80x9cxcex3xe2x80x2 and/or xcex3xe2x80x3 structural hardeningxe2x80x9d type which exhibits good creep strength and which, preferably, has good blackenability.
For this purpose, the subject of the invention is a process for manufacturing a strip made of an Fexe2x80x94Ni alloy of the xe2x80x9cxcex3xe2x80x2 and/or xcex3xe2x80x3 structural hardeningxe2x80x9d type, the thermal expansion coefficient between 20xc2x0 C. and 150xc2x0 C. of which is less than 7xc3x9710xe2x88x926/K, in which:
a hot strip is manufactured either by hot rolling a semi-finished product or by direct casting of a thin strip which is optionally lightly hot-rolled, and the hot strip is subjected to a softening annealing operation consisting of a soak between 950xc2x0 C. and 1200xc2x0 C. followed by rapid cooling and optionally a pickling operation, in order to obtain a softened strip;
a cold-worked strip is manufactured by cold rolling the said softened strip, with a reduction ratio of greater than 5%; and
the cold-worked strip is subjected to a recrystallization annealing operation in an inert or reducing atmosphere, carried out either on the run with a residence time between 900xc2x0 C. and 1200xc2x0 C. of between 30 s and 5 min, or statically with a soak at a temperature of between 900xc2x0 C. and 1050xc2x0 C. for a time of between 15 min to 5 h, followed by cooling down to a temperature below 500xc2x0 C. at a cooling rate sufficient to prevent the formation of hardening precipitates.
The invention also relates to an unhardened strip made of an Fexe2x80x94Ni alloy of the xe2x80x9cxcex3xe2x80x2 and/or xcex3xe2x80x3 structural hardeningxe2x80x9d type, the thermal expansion coefficient between 20xc2x0 C. and 150xc2x0 C. of which is less than 7xc3x9710xe2x88x926/K, which after hardening by the precipitation of xcex3xe2x80x2 and/or xcex3xe2x80x3 phases has a yield strength greater than 600 MPa and a creep resistance at 600xc2x0 C. for 1 hour at 350 MPa characterized by a creep strain of less than 0.2%, and at least one side of which optionally includes a uniform gold-coloured layer.